Industrial guns have found increasing use in situations where it is necessary or desirable to dislodge equipment obstructions at fairly large distances from the interiors of heated equipment where it would be unsafe for humans to enter into the equipment to dislodge the obstructions. For example, industrial 8 gauge guns are currently used to dislodge rings or residue which form in kilns rather than have to allow the kiln to cool off so that personnel can enter the interior of the kiln to dislodge these rings. In this way, the kiln can be kept at an elevated temperature to avoid reheating expenses and time and the rings can be dislodged by shooting them off, piece by piece, with gun projectiles. In most cases, cylindrical-shaped projectiles fired one at a time are used rather than multiple projectiles or shot. These industrial guns using 8 gauge or larger cartridges produce such large recoil that they are not handheld but rather are conventionally mounted on stands adjacent the opening of the kiln. From this position they are fired into the kiln to dislodge the obstructions. It may take literally thousands of rounds to ultimately dislodge the entire obstruction. The conventional industrial gun has a lever actuated dropping breech block and a lanyard operated trigger. This requires two people for fast operation since two hands are needed to operate the breech block lever and the lanyard leaving no hands to load the shells into the gun. In order to allow single personnel operation some industrial guns have an auto-fire mechanism which automatically fires the gun when the breech block is raised to the fully upright closed breeching position. However, the number of existing lanyard operated industrial guns is such that it is desirable to design the auto-fire gun with parts that are readily interchangeable with those in the lanyard operated gun so that conversion of guns from auto-fire to lanyard operation or from lanyard operation to auto-fire operation can be rapidly accomplished. One conventional auto-fire assembly (used prior to the subject of this patent) requires substantially a complete disassembly of the lanyard operated gun in order to insert the several components of the auto-fire assembly and convert the gun to auto-fire. There is a need for an auto-fire assembly which can be more rapidly installed in lanyard operated guns in order to minimize the changeover time from lanyard operation to auto-fire operation.
The present invention solves this problem by providing a trip arm actuated by the lever which operates the breech block, the trip arm being in turn connected by a fixed-axis shaft to a trigger actuator which pushes the trigger in response to the trip arm being depressed. Thus, when the trip arm is depressed the gun fires if the trigger is in a position adjacent to the trigger actuator. The trigger actuator is located on the gun in such a position that the trigger lies adjacent to the trigger actuator only when the breech block is in its fully upright closed breeching position in order to prevent firing of the gun when the breech block is not in that position.